The new Bus Status visual feedback is a great addition! I remember that when I got started with Wwise I was confused about bus statuses as there wasn't much feedback in the GUI to indicate what a bus was actually doing. There seems to be a little bug where if you add/remove Metadata to a bus, its status and icon are not immediately updated - I entered a report for this.
In terms of Metadata, at first I found it a bit confusing that you can instance it on both Actor-Mixer Hierarchy containers and Master-Mixer Hierarchy busses but now that I played with it a bit more it makes sense and it looks like a very flexible solution.
Initially I didn't understand what the "Use Default" Mix Behavior meant, but I now noticed the default behaviour is driven by the Positioning settings of the container. As it seems like the System Output Metadata and Positioning settings are intertwined, I wonder if designers would find it easier if those settings were grouped under the same Positioning tab - ultimately, 3D sound settings are still related to the Positional behaviour of a sound. I can imagine though that more fields will be available for customisation in the Metadata tab in the future, so there may be reasons that I haven't considered for how it's currently set up.
Thinking about the implementation of 3D audio in my work project, I believe it would be helpful if the Metadata Mix Behaviour were available to set via an RTPC. If for example we had an Actor-Mixer container for all FPS weapons sounds in the game, it would be great if we could allow the player's weapons to use Passthrough, and all NPC/other players' weapons to use audio objects instead.
Ultimately, I think it'd be great if there was a certification course for Wwise and 3D audio: the topic is still very new, quite complex, and there isn't yet much documentation available. I believe that having a thorough course focused on it would be beneficial to lots of game audio workers.